bugfix: correctly auto fix when there are multiple export specifiers

[kazushisan]

This PR will fix the behavior of ts-remove-unused's auto-fix when there are multiple export specifiers that need to be removed

const d = 'd';
const unused = 'unused';
const unused2 = 'unused2';
export { d, unused, unused2 };

Cause

ts-remove-unused calculates the necessary text change ranges using the same ts.SourceFile obtained at the beginning of the modification. For most cases this is sufficient however when there are multiple export specifiers, the text change range conflicts with each other. For such case, I've added a step to abort getTextChanges and update ts.SourceFile in the language service before continuing with the modification